Spatiotemporal dynamics of satellite-derived chlorophyll-a in the Sibutu Passage, Philippines

Phytoplankton play a vital role in marine ecosystems as primary producers, and their biomass, represented by chlorophyll-a (Chl-a), reflects ocean productivity influenced by sea surface temperature (SST), monsoon activity, and ocean circulation. This study analyzed the spatial and temporal variability of satellite-derived Chl-a and SST across the Sibutu Passage, southern Philippines, over the annual cycle of 2024. Monthly MODIS Aqua Level-3 data were processed using QGIS for spatial mapping and Google Earth Engine for temporal mean extraction. Results showed that Chl-a concentrations ranged from 0.14–0.26 mg m⁻³, with higher values during the northeast monsoon (January–February) and lower values during the southwest monsoon (September–October). SST varied 27.9 °C to 30.8 °C, exhibiting an inverse relationship with Chl-a. Pearson correlation analysis indicated a moderate inverse relationship between Chl-a and sea surface temperature (r = –0.44); however, the relationship was not statistically significant (p = 0.15). The observed inverse trend is suggestive but not statistically confirmed, likely due to the limited sample size (n = 12 monthly observations from a single year), which reduces the statistical power of the analysis. These patterns suggest that monsoon-driven mixing and seasonal thermal stratification may influence phytoplankton variability in the passage. As the analysis is based on a single year of observations, the results primarily reflect seasonal dynamics rather than long-term climatic trends. Despite generally low surface productivity, localized mixing processes within the Sibutu Passage may contribute to enhanced biological productivity in this inter-basin marine corridor. These findings provide a preliminary satellite-based productivity baseline for this understudied region and highlight the need for longer time-series observations and in-situ oceanographic measurements.